AN443 APPLICATION NOTE

6/14

Solving we find

In the previous example this condition should be

It is obvious that this condition is generally very difficult to meet without hard selection.

TRANSIENT VOLTAGE SHARING

The problem

When a diode is switched from the forward conduction to the reverse blocking state, a reverse current

flows through the device during the reverse recovery time trr.

After this delay all the charges (minority carriers) stored in the junction are eliminated and the diode turns

Figure 6 defines the reverse recovery parameters. When a string of n diodes in series switches off, the

diode which has the lowest recovery charge turns off first and supports an important proportion of the total

Figure 6. Reverse recovery current waveform

Voltage sharing during the reverse recovery phase is achieved by using a shunt capacitor string connect-

ed across the diodes (see Figure 7).

∆I

R

I

RM

---------

1k

–

() nV

RRM

V

M

–

()

V

–

()

-------------------------------------------------------

<

∆I

R

I

RM

---------

5%

=

QRR

t

I

IF

dIF/dt

t

RR

0